there was a small room （served as a kitchen ）做定语修饰room ,房间和serve（当做.使用,用做）之间是被动关系,所以选BD选项 in which=where 相当于是副词做状语,若选d in which served as a kitchen ——— ——...为什么说是副词做状语！？副词一般在句子中做状语．而且这道题如果选d的话，应该是把它考虑成定语从句了，在定语从句中 in which=where，where 为关系副词后接主谓宾齐全的句子例如：this is the factory where i worked. this is the factorywhich i saw yesterday